This invention relates to a method of exciting an a.c. generating means such as an a.c. generator and an a.c. welder.
Typical conventional methods of exciting a.c. generating means, for example a.c. generators are as shown in FIGS. 1 and 2. In the method illustrated in FIG. 1, electric currents are obtained from three phase outputs U, V and W connected to an armature winding Am through a current transformer CT, and electric currents are obtained through reactors L from the three phase outputs U, V and W. These currents thus obtained are rectified by a rectifier Rect and applied to a field winding Fc.
However, the arrangement of the a.c. generator is disadvantageous in the following points: The generator is liable to become bulky and high in manufacturing cost. If the load is a pump under water, a winch, a motor-driven compressor, etc. with the generator and its exciting device designed small in size, then the transient characteristic becomes unstable, and at worst it may be impossible to supply current. In order to overcome this difficulty, it is necessary to employ an a.c. generator having a larger capacity.
In the method illustrated in FIG. 2, only a zero phase current from the open ends of a delta-connected winding is rectified by a rectifier Rect and applied to a field winding Fc. However, since it is impossible to cover the exciting current with the zero phase current only, the method involves a number of problems to be solved before it is actually practiced.